Excel:

Formula to create some kind of composite ID with random number (incl leading 0) date and letters

= INT(RAND()*1000)

=H9&CONCATENATE(TEXT(TODAY(),"yymmdd")&TEXT(I9,"000"))

Where H9 contains 'ST', I9 contains random number. I could be made as on liner, but - still.. not a big hassle.

MS Access:

For preexisting -  data has to be imported (this column)

For future (new ones) to follow the pattern below has to be defined for this 

column, and it'll create automatically:

MS Access (design view)

column in the table properties (default Value):

='ST' & Format(Now(), 'yymmdd') & Format(Rnd()*1000), '000')

Indexed (?):

YES (No Duplicates)