No - No - No ! Please don't take this awesome information exchange underground. Unless of course there's really private stuff.
These are not tedious or obscure cloggings. Information mining by you learned researchers is one of the the great attractions of Prune whether we bystanders have a personal interest or not.
Us amateurs who might aspire to occasionally offering something modestly useful or half accurate to these pages (see below for an example) iive in awe of threads such as this.
Here you have a respected and learned OP who appears to have exhausted this particular bit of research and within 24 hours, up comes the most comprehensive answer one might have wished for, plus what promises to be a further fertile source. It seems likely that neither source might have been "published" but for Laurence's original inquiry.
Two minor points to offer if I may - that may already have been covered or well known.
1. The National Archives at Kew appears to hold a file on 70 OTU - which you may well have tried
http://discovery.nationalarchives.go...ails/r/C754446
2. An 'airframe number' (L1234 or PR123 etc) stays with the airframe during its entire life. Noting that 70 OTU appeared not to have a specific Unit ID Code (often a two letter code) the two digit 'side numbers' that in this case are used to identify different aircraft solely while on 70 OTU, would be painted on when the aircraft arrives on the unit and would be re-used when the aircraft leaves or is written off, crashed or SOC.
Thus it would be theoretically possible for L1234 with Side No 56, to be destroyed in the morning, replaced at lunchtime by L4321 from the MU on the other side of the field - painted No 56 in the afternoon and be on night flying as No 56, but as a completely different aircraft/airframe number. Thus it would be possible for Side No 56 to be written off and reused several times, though airframe L1234 could only be written off once and would not be reused except in exceptional circumstances.
Not all aircrew personal logbooks would show both the airframe and side number. Mine didn't because I couldn't write that small for the space provided, and because I didn't know any better at the time.
LFH