"AMMs are originally numbered 0 280 212 nnn.
In your case it would be 0 280 212 001.

Later this was changed to an "Exchange" number such as "AMSnnnX".
For example AMS002X for '83 and '84 240s, and AMX007X for later 240s as well as 740 B230F and turbo variants through 1989."

On the message from Lucid above, note that the later move to "AMS" or "AMX" numeration apparently means that the unit has been rebuilt. This is particularly is useful if you see such AMM numbering at the PNP, as you'll know the unit has already been rebuilt once. I believe a similar exchanged/rebuilt numeric system is in use with rebuilt alternators.

To clarify that later system, "AMS002X" above translates to "Air Mass Sensor", "002", "eXchanged" (or "R" for "rebuilt" - AMS002R).

See the present day FCP AMM page below for a modern day illustration.

Link: http://www.fcpeuro.com/products/volvo-mass-air-flow-sensor-240-740-760-780-940

Finally, the perceived most latest up-to-date version of the 240 series AMM "0280212016" has itself been updated to "0986280101".