> No idea. I wasn't even aware that RPC had sequence numbers.

It doesn't.  Someone probably mistook the transaction ID for a sequence
number (perhaps because some implementation happens to use sequentially
increasing XIDs).

See RFC1831 - especially page 10 - for full details.

/~\ The ASCII				der Mouse
\ / Ribbon Campaign
 X  Against HTML	       mouse@rodents.montreal.qc.ca
/ \ Email!	     7D C8 61 52 5D E7 2D 39  4E F1 31 3E E8 B3 27 4B