I can't find the other thread you made for adding serial numbers anywhere on BF. The search function here SUCKS so bad so I'll add this one here.

Hub says 71. Serial is 3446705

21" Step-through frame

It took me a long time to find it and without your site showing where it should be I would never have guessed there was a serial number in that location. Only with magnification and playing with the shadows with a bright LED light can the numbers be teased out. The serial number is there but it is absolutely worthless other than for us collectors as nobody would ever see it there.

I'm assuming this is a '72 model