I feel like for a lot of their songs they would just work off the multitracks / project file of the song or whatever the proper term is of a successful song they made, use the same instruments / patches that were already there in the original to get the idea down, and then add in new instruments or replace ones if needed. It would explain why some sounds are hard to recreate because they could've taken ages to create but from there they would easily be able to just grab it from another song. It would explain why this demo of "I Will Be There" (
https://www.youtube.com/watch?v=zU8PjfXhWw8) has the same instrument sounds / patterns as BOMT, as well as why some songs, like -
Britney Spears - ...Baby One More Time
Britney Spears - Crazy [The Stop Remix!]
Britney Spears - Oops!... I Did It Again (maybe)
Britney Spears - Stronger
share (possibly, in the case of Oops!) some of the same guitar track with the same licks, especially with BOMT, OIDIA and Stronger sharing an extremely similar snare sound, as well as all the other stuff sounding really close i.e. hits, windchimes, and that one suction noise in OIDIA and Stronger.