Prior to May 2011, the validity and time limit of ITAS and ITAP were only slightly different than posterior to UU 6/2011, and this a lot of persons seem to have forgotten or perhaps simply ignore it.
With UU 9/1992 and the Peraturan Pemerintah implementing it an ITAS was valid for one year and LIMITED to 5 extensions.
An ITAP was valid for 5 years but already also "un-limited" since neither the UU nor the PP had set a maximum amount of perpanjangan/extensions. However, the lack of proper implementing regulations was making the ITAP a privilege only attained by few. But it was un-limited. Basically you could have cumulated ITAP after ITAP till you die.
Prior to 2011, the real difference is that it was as clear as mud for almost all potential applicant and a huge majority of Immigration officers of who was entitled to what and how to process their permits.
In 2007 (prior to 2007 for memory those married to an Indonesian female spouse had no residency right) for my first ITAS sponsored by my wife I had to research in Jakarta all laws, PP, Permen, Imigrasi guidelines, dll then bring them back to my kanim, insisting (a huge euphemism) to get the things verified and done. Honestly I have loved this time. Anything you were achieving was triggering a proper celebration.

After 2011 all became much, much easier. Before 2011 you had to be particularly resilient due to the amount of frustrations you had to face to get your rights respected.
UU 6/2011 was not that revolutionary in the sense that it didn't created an un-limited ITAP as some seem to think.
It's just that the publicity made around it, and the opacity surrounding the previous UU 9/1992 which had many believing the "myth" of a new unlimited ITAP vs one which would be an old one with a limit. Also the fact that Immigrants often hear what they want to hear or want to believe.
However, UU 6/2011, in my point of few, revolutionized the MINDSET of Immigration officer toward those of us married to an Indonesian spouse, and clarified drastically the procedures. Also it came with "intensive" socialization and better training of officers. This is where it has been truly revolutionary.
Back in 2011 I remember many discussions with foreigners saying how nice UU 6/2011 was because it was allowing foreign spouse to get an ITAP and an "unlimited ITAP" on top of that, blablabla. No one really tried to understand the meaning of "un-limited", or even if it was true or a novelty.
The difference in the procedure pre-2011 and post 2011 is the fact that you now only need to "report" (I love that word and it always bring me a smile because it is another BS since it's basically the very same procedure than for an ITAP extensions before 2011 and the extensions of your first ITAP) and that it's "free" (well, the report/extension is free but the MERP isn't and is mandatory). But not much else. Oh no, it's also much more expensive for the ITAP which perhaps explains why vocabulary around this ITAP is now sugar coated with layers of "unlimited" and "free"

. For reference I paid my ITAP 3.000.000 and ITAP extensions were at the time Rp 2.000.000 (extensions were cheaper than 1st ITAP) and a 2 years MERP was 1.750.000.
My first "report" was super smooth but it's more due to the fact that the competence and knowledge of Immigration officers has drastically increased since my first ITAP extension or alih status ITAS menjadi ITAP than by a change of procedures to be honest.
Also perhaps the fact that I am ageing and that people here have consideration for elders, even if I am only in my 50's.