A current-tech P25 site will step back from TDMA to non-TDMA on a talkgroup if any of the "subscriber units" affiliated to it are incapable of the current P25 standard (i.e. TDMA). I don't believe they can be configured to drop further back to analog since an analog radio wouldn't work on a P25 system of any vintage (don't be confused by Motorola Type II systems that have a few TGs with P25 audio ... like most of the legacy OKWIN sites!).
So if there is an old radio on a talkgroup, your non-TDMA scanner will hear it fine.
Just buy a P2 and you'll be fine (and, as a bonus, can buy the capability of DMR and NXDN as well).