[R-390] Incomplete IF module

[Glenn Little WB4UIV]

Some years ago I bought an incomplete IF module from a surplus house. In 
cleaning this weekend, I uncovered it.

The module is marked
SM-C-343621
I.F. FINAL ASS'Y
FR-11-C22-C-4-26418(E)
SER. NO. 0294

The module has the tube sockets, RF connectors, T5-1-T503, Z501, C506, 
TB501 and some small parts mounted. Very little has solder on it.

Is this a rare find?

Why would it have the serial number assigned before completion?

Thanks
73
Glenn
WB4UIV