I’d say in both cases “0.9” is the version and /alpha-?/ is the priority
modifier, so if one is '(0 9 -3) then they both should be.

Two other options for dealing with these cases (while keeping
“OTP-18.0.5” -> '(18 0 5)) is to just strip the /alpha-?/ and parse
those strings as '(0 9) or flag them as invalid version-strings.  My
ordered preferences are:

1. parse them both as '(0 9 -3)
2. treat them as invalid and throw an error
3. parse them as '(0 9)

FWIW, attaching the diff for (1).