There were 17 official printings of this book, though printings 6 to 10 all say "6th printing".
There are many variations within the print runs. TSR, especially in the early days, was notoriously frugal with their print runs, resulting in every part that could go out doing so. When something ran out, substitutions were made as deadlines had to be hit, especially those dictated by an event. When bits were left over, they were used early on the next print run. Expediency won out over consistency.
Compounding this is the fact that printing a hardback book, especially in the 1970s with a smaller press, is a multi-step process covering several parts and involving human labor in every step of the way. One cannot assume that even the same amount of pages will be printed of every page!
These printed pages must be folded, stitched, attached to their backing, inserted into the cover and attached to the endpapers. The pages must be trimmed so the edges are even. The covers have their own printing and assembly process. There are so many variables in these processes that if all quantities come within 5 percent of each other it's considered a success. The size of the print run is dictated by which part runs out first. Hopefully that's at least as many as were ordered. It is both to the printer's and the publisher's advantage that parts don't get wasted if budget and quantity are the primary concerns.
As TSR got bigger (and more professional) things like this happened less and less often. Later printings are much more consistent throughout.
It's things like this that keep collectors up at night.
1st: "ADVANCED DUNGEONS & DRAGONS" centered at top of cover, "PLAYERS HANDBOOK" centered in lower middle of cover, no printing info on title page. Some early versions printed up for GenCon had white flyleaves. The rest had goldenrod flyleaves.
2nd: "ADVANCED DUNGEONS & DRAGONS" centered at top of cover, "PLAYERS HANDBOOK" centered in lower middle of cover, "2nd Printing" on title page.
3rd: "ADVANCED DUNGEONS & DRAGONS" centered at top of cover, "PLAYERS HANDBOOK" centered in lower middle of cover, "3rd Printing" on title page.
4th: "ADVANCED DUNGEONS & DRAGONS" on yellow band in upper left corner, "PLAYERS HANDBOOK" centered at top of cover, "4th Printing" on title page.
5th: "ADVANCED DUNGEONS & DRAGONS" on yellow band in upper left corner, "PLAYERS HANDBOOK" centered at top of cover, "5th Printing" on title page.
6th: "ADVANCED DUNGEONS & DRAGONS" on yellow band in upper left corner, "PLAYERS HANDBOOK" centered at top of cover, "6th Printing" on title page. At one point the white flyleaves return
So far, nice and straight forward. However, at this point TSR quit updating the printing info until the 11th printing.
(Why? Unknown, but this coincided with the distribution deal with Random House. While pure speculation, it's possible that the deal covered only certain editions of the books (within the whole of the AD&D line at the time) and TSR therefore quit updating the printing info)
7th: Face logo on front
8th: new cover art, but D.A. Trampier still listed as artist
9th: TSR Hobbies --> TSR, Inc. Jeff Easley is now credited for cover art
10th: Rear cover adds the price ($15.00)
11th: Print info is corrected to say 11th printing!
Beyond this the printing info is correct on the title page
Hybrid editions: these do exist, as implied by the notes on printing procedures. Nothing so obvious as the Monster Manual with the "3rd Edition" interior with a mish mash of the 3rd and 4th edition cover (obviously this was deliberate as the cover required a completely separate printing on its own), but leftover parts from one printing would make it into the next. The easiest ones to spot are late 3rd Printings that have some some of the 16-page signatures replaced with those from the 4th printing, as the intermittent shading will be apparent. It's unknown how many of these were made nor whether they were even deliberate on the part of TSR.