Here is my collection of 1st generation Simplex 4251-20s (without the arrow). The one on the left seems to have a different sticker for the model number, along with a handwritten serial number vs the other two having a printed serial number.
I’ve never seen a first gen 4251-20 with that label either, must be extremely early in the production run.
fun fact: the buttons in these were changed to the plastic ones we see today because they can actually get stuck in the depressed condition under the correct conditions!
I have owned a fair number of these over the past couple months. Four 4251-20s, and I most recently bought a 4251-50. I’ll attach a few photos.
