Ok dudes,
having been Se obsessed, esp mids chool for many years now, here's what I understand to be the timeline - the straight stay pk ripper with the integrated seatclamp was 1985 for one year only. Imn 86 they introduced the curvy chainstays and thats the way it stayed until 1991 - and in 1991 they introced the Pitbull mount pk ripper in two sizes - I have both sizes still - one with a 20.5" pro tobtube, one with a 21" pro XL toptube.
There is a grey area around 1990 when they may have introced a 20.5 or 21" toptube curvy chainstay pk ripper with regular caliper mount, just before the pitbull mount ripper came out in 91. The pitbull ripper hung around until about 1994 when the frame went from 1" to 1.1/8" and they added canti mounts on the rear.
Around this time of 94/95 SE were doing small numbers of frames with weird combinations of headtubes/brake mounts as they were using up old stock I guess and bridging the gap between 1" and oversized and from caliper to cantilever - so dont be surprised if you find a 1" headtube bike with canti mounts, or a 1.1/8" headtube pk with pitbull mounts.
i myself had a pitbull mount pk ripper that had a very strange headtube - it was essentially an oversize 1.1/8" headtube that had a shim inside it to reduce it down to a 1" headtube fitting, and this was a factory frame - not second hand botch. very interesting!
In 95 ish onwards they had the pkr ipper xl and the pro length until 1997/8 when Se went overseas with some of their frame production , but before it was sold to Fuji Bicycles and became the Se we know today.
The Pro XL pk riipper was stil produced in 1999 in asia, and you can tell these from the serial numbers - I have one here - they basically had their floval tubesets and designs replicated out in asia - so the frames look identical to the us made ones from a year or so before. The Asian pk ripper from 1999 had the larghe SE downtube decals, and normall one or two serial numbers - one is on the top of the bb shell [as if youre looking down when riding, itd be on your left or right on top of the bb shell] and normally started with the letters IS [possibly for International Standard whcich the US bb was then] and then some numbers.
Other models also had a serial number on the underneath of the bb shell too, but not all.
Hope ive helped!
steve