ADPATCH: Does anybody aware what “load Package Revision Information” step is for?

Hello Community !

Question about ADPATCH.

Does any body aware what "load Package Revision Information" process is
for?
It is a phase in a patch apply process.
In our environment this step takes ~30 min.
Interesting that it isn't fared always.
ADPATCH loads packages revision data just for same patches.
I know that during that process Oracle reads packages' versions using SQL
like one below from a database and store this information in a files system
for a future use.
select owner,
       substr(text,instr(text,'$Header: '),
              ((instr(text,' $',instr(text,'$HEADER: ')) +2 )
                -instr(text,'$Header: '))
             )
    from dba_objects
    where line=2
        and text like '%$Header: % $%';
.
Data in the Files System called "Packages' revision cache".
I know that we can use "norevcache" option of adpatch for avoiding that
phase.
==================================================
    * revcache              - To load the package revision cache (if
                              adpatch
                              determines it is needed).
                              Default - revcache.
==================================================

Question is: Is it safe? What Oracle does in case "Packages' revision
cache" wasn't refreshed?
Does Oracle read version information from Packages' source files located
under $MOD_TOP/patch/115/sql/ directory or it uses old cache data?
Is there way to refresh it manually before a patch apply process in order
to minimize system unavailability time?
Where Oracle stores revision information?

You input would be more than appreciated!
Thank you in advance,
Yury

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