If they're using <majorVersion#>.<minorVersion#>, 51 would be lower/older than 101. And I see no 1.51 listed in the Fastlane changelog file (notes.txt). The oldest version listed is 1.112 and there is a jump from 1.114 to 2.5 nothing in between)
1.51 sounds like the version that added stuff like LRRP and NXDN talkgroup and radio ID decoding. There were threads about it maybe 18 months ago?
But if the OP is looking for D-Star voice decoding in DSD+, yes, the changelog has that showing up in 1.112