Early? NET&T L&LD sign

[Sargeguy]

Just acquired this sign. The steel is lighter gauge than my other ING-RICH flat NET&T L&LD sign and the rear in not fully enameled. Also the porcelain is not as consistent, there are tiny flecks of blue in the white field.  For this reason I suspect it may be an earlier sign.

[Sargeguy]

Here is the other one for comparison purposes:

[RotarDad]

Nice signs, Greg.  Question:  Why does the newer one have no mounting holes?  Was this mounted in a frame of some kind?  It would seem they would all have holes for different mounting options.  Thanks for the ongoing education with these!

[Sargeguy]

My current thinking is that the one with no holes was used in a sign like the one below.  It is much more rigid than the other flat signs. I think it was made that way so it wouldn't flex out of the frame.