I question your dates Random Guy.
My L42A1 is one of 22 rifles converted in the very first batch of rifles after the trials was completed. Conversion date 2-25-1970
...I am certainly
not an Enfield expert. My reading of the following book suggests that the first 30 experimental rifles with different length barrels, twist rates, etc were delivered in early 1970. These 30 rifles were marked "XL42 E1." (XL designating experimental item).
Assuming this reference is book is correct (based on the archives at RSAF Enfield) , a February 1970 conversion date corresponds with the first batch of 30 experimental rifles marked "XL42E1" delivered to the ITDU (infantry trails development unit), so I presume you have a rare rifle with either an "XL" prefix, or per this book, had many had the "XL42E1" grinded away 'quite robustly' and have a deep scallop that is present on the side of the receiver, and re-engraved over that same area L42A1. (See below pic and text). T.he book doesn't say exactly what happened to the 30 trial rifles, but it notes some of these trial rifles are in the hands of collectors.
Apparently 30 of the first 'standardized' L42A1 type rifles were not delivered to thte military as one might expect, but were delivered in December 1970 to the Metropolitan Police. The Police Dept rejected all of them over various issues or what they considered to be defects. Two senior Enfield armourers subsequently went to the Metropolitan Police station and inspected them in January 1971. They found that 12 of them did indeed have defects. (The serial numbers of those 12 are listed in this book). The other 18 'rejections' were due to the Police dept "not being familiar with the standards specified in the conversion program and their inexperience as to the methods of sight adjustment." The police ultimately rejected the program.
The first military (ie, "MoD" ) L42A1s were recorded as delivered to Donnington in January 1971, the same year that the majority were delivered. Smaller batches of MoD rifles were: "delivered to Donnington in 1972, 1974, 1975, 1977, 1978 and 1979 and spuriously 1980.."
...again, the reference book I have states "The Lion's share of the MoD contract was fulfilled in 1971 and the vast majority of examples today carry a 1971 conversion date." It notes the only rifles delivered in 1970 were 30 experimental rifles for military trials (circa Feb 1970 thru August 1970), and 30 of the new/standardized L42A1s were sent to the Metropolitan Police in Dec 1970 - which were summarily rejected, of which 12 were likely re-worked upon inspection. It is not clear in the text, but it seems possible that the rejected police rifles were subsequently provided to the UK military in January 1971...but that is my conjecture/reading of the above except.
My reading is that the NSN was created in August 1970 when the rifle was approved for the military service. In January 1971 the Royal Marines got their first batch of M42A1s. Again, I am not an expert on Enfields, I was referencing the dates in the above book by Steve Houghton.
Would like to see your L42A1 if you have pictures...they are historically interesting and valuable rifles...