Yes that would be the reason! I remember really questioning my ability to restore the MG Midget back then. I was also very worried about the rear suspension mount but it looked like the rust had stopped just before the join.
Well I stuck to what I had learnt so far, cut out the old and make or buy a new panel and weld it in...simple!
I cut a 32cm x 2.5 cms length and copied the curve
Once the curve was correct I marked out the flange which welds to the floor panel...
...and welded the two together
Then I offered it up and it fitted well
Before welding it I had to make sure it was perfectly level with the rear suspension mounts
All welded in and looking much better!