Following description can be found in Ubuntu Software Center (Ubuntu 16.04 LTS) for Automake package:
Automake 1.15 fails to work in a number of situations that Automake 1.4, 1.6, 1.7, 1.8, 1.9, 1.10, 1.11 and 1.14 did, so previous versions are available as separate packages.
Few questions arise from this:
Why are versions 1.12 and 1.13 not mentioned in the list?
Fact that 1.15 fails to work in a number of situation - is this a problem of Automake or integration-in-Ubuntu's one?
Description mentions previous versions are available as separate packages - where is that availability, GNU or other automake distribution servers or Ubuntu packages distribution system?
All of those packages should be available in Ubuntu, for example as
automake-1.14.As for the fails to work in a number of situations comment, I would expect it's likely because Automake 1.15 changed something which broke compatibility, which has been common in the past.
As to why certain versions aren't listed there, that'd be a question that only the specific person who packaged automake (probably a Debian developer) could answer. Changes to packages in Ubuntu usually don't alter the package description, and you can see Debian has the same description.