Incremental TeX-Live ?

[Philip Taylor]

Over the years I have installed every version of TeX Live from 2008 to 
2021 (pre-test), and keep older versions to help in identifying the 
cause of malfunctions when an older source file is compiled with a more 
recent version of TeX Live.  But I realised today, as I was installing 
the most recent instantation of TeX Live 2020, that by now I must have 
(probably) hundreds of thousands of duplicate files.  While it may well 
be the case that only 10% of the files in TeX Live 2008 appear unchanged 
in TeX Live 2021 (pre-test), it seems equally likely that perhaps 90% of 
the files in TeX Live 2020 appear unchanged in TeX Live 2021 
(pre-test).  That being the case, it seems to me that there is zero 
benefit in re-installing for TeX Live nnnn+1 any file that appeared 
identically in TeX Live nnnn.  So, a couple of questions :

 1. Do the resident experts agree that if my TeX search path(s)
    contained the root directory of each installation of TeX Live from
    (in my case) 2008 to 2021 (pre-test), then any TeX binary in TeX
    Live 2021 (pre-test) would find the necessary support files no
    matter where (in that set of directory hierarchies) the last
    installed version of that support file was to be found ?

and if so :

         2. Would there be any benefit in enhancing the installer to 
look for previous versions of TeX Live, and if such exist, not 
duplicating (i.e., re-installing) any file that existed unchanged in an 
earlier release ?

Clearly if the answer to (2) were "yes", then the installer would also 
have to ensure that the earlier versions also appeared (in the correct 
order) in the TeX search path(s), but overall it seems to me that 
considerable time could be saved when performing a full install if the 
previous year's files could be used (when unchanged in the most recent 
year) rather than installing a fresh-but-unchanged copy.
-- 
/Philip Taylor/

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