Different date code on my German MP5 receiver and bbl, etcc

[MP5]

The date date code of my Pre-86 German MP5 is IF, for (I believe) 1985. The bolt is also date coded IF, actually it shows IF 092. Is there any significance to the 092 numbers after the IF? Anyone know what the SP on the bolt means? The bbl is date coded IE 1L. (1984 .... what is the significance of the 1L?) Is it common for a bbl to be date coded the year prior to the receiver? I'm 99.99% sure this is an all original gun, I got it from a PD in 1990, and the original transfer paperwork from H&K to the PD was dated 1985, so they didn't have it long and I doubt they changed anything out. I'm guessing that the H&K armorer at the factory just grabbed a bbl off his rack that was date coded one year prior to the receiver he was working on. Can anyone confirm this was commonplace? (The trigger group also has a [1984?] date code on it of 3IE.)