Its actually Dot 2,3,4 and 5.1 thats are all interchangable, Dot 5 is the syn stuff that must not go with the std stuff, requires full system flush, new seals etc before use in an existing system
Perfectly simple numbering system ####ed up by some dimwit
In its simplest form, suck m/cyl res empty then refill, dozen pumps each corner done