Two Character Codes On Backs On 1970-S Covers

Though the info suggests MPLSMs were used into the 1990s I recall looking for LSM codes that decade and finding none. It could be that the code stamping part of the process was eliminated before the machines were.

FDCs might have usually received special handling since I could not find a single LSM code on mine, even those that went through the mail during the 1970s, the decade during which I believe LSM coding to have peaked. Non-FDCs may offer more clues.

The most recent LSM code use I found during a quick flip through some old letters was on one postmarked Feb 4, 1988. This was only a small batch of letters, so the codes certainly were in use beyond that date.