Now, does that mean they changed typewriters in the middle of a word? Probably not, but they did change the location where certain items were typed.
Irey would need to demonstrate that everything typed at the BOH office, including other forms typed at the same time (they exist), do not show that characteristic.
Throughout this particular debate I've assumed both machines were electric typewriters. However, the typewriter at the hospital in the Birthing Center may have been a manual. In that case you would EXPECT differences to occur in typing due to the typist pressing the keys with different pressure ~ particularly if the typist's primary job was not, for example, typing, but, instead carrying babys around.
Maybe Irey has done nothing but prove the nature of the environment and the type of typewriter used (manual vs. electric).
Irey's examination shows many beaucoup "a" impressions that he thinks are different enough for us to be interested in. Lo and Behold, the "a" on the keyboard is pressed by the little finger on the lefthand and that's usually the weakest carpel in the bunch.
That means Irey's discovery is highly probable if one of the typewriters used to prepare the document was a manual!
Yes, you did suggest something, that the form was filled out on different machines at different times. But the discrepancies appear on the same lines and within the same words. Either your speculation is BS or they switched machines in the middle of individual words. There is no other way to explain it.