on some of the boots i've been getting most of the tracks are marked as "take #". but some of them have "RS#" or "RM#" instead of (sometimes as well as) a take number. what do this mean?

RM = Remix from multi-track tape to mono
RS = Remix from multi-track tape to stereo
SI = Superimposition, same as overdub (a technique used by recording studios to add a supplementary recorded sound to a previously recorded performance.)

so if there is a tap number, than it's a mixdown from that tape, i'm assuming. if there is not take number, is it from the same take(s) that's on the record? also, i guess that means RM1 is the first mixdown and then RM2 is the second, and so on.

Quoted from RunningMonk

so if there is a tap number, than it's a mixdown from that tape, i'm assuming. if there is not take number, is it from the same take(s) that's on the record? also, i guess that means RM1 is the first mixdown and then RM2 is the second, and so on.

This is where it gets messy.

As far as I know RM1 or RS1 if you like, would be the first mix down. Sometimes when a song was remade they would begin at 20, so you might see RM1, RM2, RM3, RM20, RM21 etc. You may also come across RS82, or RS95. That is the 1982 [Barrett] or 1995 [Anthology] remix. It can all get a bit confusing. As someone on BootlegZone said 'it's The Da Vinci Code for Beatles fans'!