Faked Scott #578.what Was This Altered From?

Recently purchased this on HipStamp. I was leary from the getgo as it looked flat plate to me. Well I was right. Scott #578 needs to be rotary press coil waste 11x10.
This stamp is narrower by .5mm.
Also the perf 10 side gauged at 10-79 whereas a genuine rotary press coil gauged 10-81.

What was this altered from? Imperf stock? To my knowledge flat plate booklet pane stamps are not as tall as compared to flat plate sheet stamps.

Anyways this will be return for a refund.

It could have been made from a jumbo 552. And since it might have been done any time in the last 90 or so years, it would have simply been thought of as a cheap stamp with large margins.