You will find the following "term":
?Mixed stacking (stacking one or more of the BPS 2000, BayStack
470-24T, or the BayStack 460-24T, with the BayStack 450, but NO
in the release notes for BoSS 3.0 (name of the sw for BPS/460/470)
You need to follow some rules, also covered in the same doc.
(like, the BS450 need to be running software version 126.96.36.199, and there
is some requirements about the sequence in the stack).