Please, what does the quoted reference actually mean, thanks ?

Its just a reference to identify the set of Parish records ( i.e. a Register)

Am I correct in believing there wasn't a "standardised" way of recording such things as there might perhpaps be nowadays, and these varied between different Parishes and areas ?.

Correct it varies by Parish , by time etc
http://www.forum.forest-of-dean.net/index.php?id=25449