The online book is about the best reference there is at the moment, but it's very much a moving target.
As Starchild mentioned, you can get credit for the patch by turning west in Harriman and hiking the A-T over to High Point, then heading north on the Shawangunk Ridge Trail to where it rejoins the NY LP. Otherwise, you'll have about a hundred miles of what amounts to a roadwalk through suburbia. (The Orange County Problem: there just isn't any place to clear a trail corridor any more.) The best they've been able to do with the Orange County route is to put a lot of it on paved rail-trails.
On the other hand, the Catskill sections are much improved in recent years. It's become a terrific trail from Riggsville nearly to the Schoharie Reservoir. Several long roadwalks have been eliminated, and the trails that replace them (Cross Mountain-Romer Mountain, Phoenicia-Warner Creek) are wonderful. It's a hundred miles that any hiker will love, particularly if they like tough trails. Burroughs Range, Devil's Path, and the north side of Blackhead all have rock scrambles comparable with anything you'll find on any of the 'big name' trails. But the last time I checked, even the online book is out of date with respect to those sections.
A few recent relocations (hastily edited in the online book, but not all the descriptions seem to hook up correctly):
Section 19 (Wittenberg-Phoenicia) is totally different. Once you've summitted Witttenberg and are on your way down to Woodland Valley on the red-blazed Burroughs Range trail, look for a blue-blazed trail (the Cross Mountain-Romer Mountain trail heading to your right (trail north is compass south at that point!) It will take you about nine miles over Cross Mountain (2500'), just west of Mount Pleasant (2800') and over Romer Mountain (2240'), with many excellent views of the Esopus valley, bringing you out on Lane Street in Phoenicia. Turn right on Main Street, roadwalk County Road 40 for about 1.5 miles, and turn-left on the red-blazed Phoenicia trail up to the Mount Tremper fire tower, passing two lean-tos on the way. From the fire tower, blue-blazed Warner Creek trail continues north, making its way up Daley Ridge to the flat summit of Plateau Mountain. The trail there rejoins the former Long Path route, which is following the red-blazed Devil's Path. This change, which was made in two phases, cuts off a long roadwalk between Woodland Valley and the Devil's Tombstone campground. Phoenicia is a full-service trail town (several restaurants and inns, an outfitter, a supermarket, a pharmacy, a laundromat, ...) and very hiker-friendly. This is a good thing, because it will be 40 miles (and only two road crossings) before any other services. Neither of the two intervening road crossings (Platte Clove Road and NY 214) has any stores within about five miles of the crossings. The most recent (2014) phase of this relocation is documented on the NYNJTC web site (http://www.nynjtc.org/files/Catskills_LongPathRelocation-SlideMountainWilderness_TrailMap2014b.pdf). A loop hike involving the 2007 phase (http://www.nynjtc.org/hike/plateau-mountain-warner-creek-trail) is also there.
There are various mistakes (look like incomplete edits) in the page for Section 20 (Phoenicia-Sliver Hollow Notch). And the page links are all wrong, just go up to the table of contents to get to the pages in sequence. The ford of Warner Creek (expect wet feet at the very least, and a dangerous crossing at high water) is at mile 8.25, not 6.95.
In Section 27, be careful at mile 5.7, approaching Ashland Pinnacle from Richmond Mountain. The Long Path turns right on a maintained dirt road. The aqua blazes of the former Long Path route are still visible going forward, and will lead you about five miles across Huntersfield Mountain to a private property line where the landowner revoked a trail easement. (The 'General Description' of this section still has the trail going there!) While that section is a nice hike (http://dftscript.blogspot.com/2014/04/saturday-walk-2014-04-26-huntersfield.html), it won't help you in your goal of thru-hiking the Long Path!
There are current plans to move virtually the entirety of Section 15 off the road and have it head directly through the woods to Vernooy Kill Falls. This trail is awaiting approval of a new Unit Management plan for the Sundown State Forest, which is supposed to be imminent.
The end of the Northern Excursion is the start of the Northville-Placid Trail, so it's possible (and has been done) to thru-hike both trails in a single long trip. If your ambition includes this, note that the southern terminus of the Northville-Placid Trail has also been relocated. It's now on Benson Road about milepost 7.5, cutting off about four miles of roadwalk. (There are plans, with trail construction under way, to move the terminus even closer to Northville. The route is mostly flagged and hikable by those with good bushwhack skills.
Overall, sections 5-6 are quite nice, and the 110 or so miles in Sections 16-28 are just gorgeous. The rest of the trail is considerably less impressive, but considerably improved in recent years. Expect a lot of roadwalking and rail-trals outside the above sections, although there are nice woods sections here and there.
Watch the guidebook descriptions closely, and carry maps in the Catskills (the NYNJTC set is quite good). In the Catskills at least, aqua blazes are few and far between, because the trail is mostly sharing treadway with other trails (Peekamoose-Table, Curtiss-Ormsbee, Burroughs Range, Cross Mountain-Romer Mountain, Warner Creek, Devil's Path, Platte Clove Preserve, Kaaterskill High Peak, Harding, Escarpment) and following their blazes.
For the middle sections, you might want to call or email Jeff Senterman (
[email protected], PM me for the phone number). He's Catskill Region Program Coordinator for NYNJTC. He's very knowledgeable about the trail. I've done some trail construction work under his supervision. (He'd also have contacts with the people on the other sections, where I'm less familiar.)