In English, first sight panel means all the visible top side of the car that has finished paintwork. This would be covered under the 3 year paintwork warranty.
The underbody of the car is not finished in paint at all (beyond the primer dip) and is covered by the 7 year rust warranty. This warranty is, as is usual, perforation only, so you have to have a hole rotted through in order to claim.
Therefore MGs response was entirely predictable. I think at this point we are flogging the proverbial dead horse. These cars, along with a lot of other marques today do show early light rusting at cut seams and around welded areas. This is mainly due to the "improved" (for the environment, not the cars!) factory dipping process that's now used, thin film zirconium. This doesn't result in large volumes of toxic heavy metals as a by product, as the previous, better (for the car, not environment!) Zinc phosphate dipping process did.
Although unsightly, this is very unlikely to progress to serious rust during the 7 year rust through warranty period. So I'd suggest those keeping the car for the usual 2 to 4 year cycle stop worrying.
Those keeping for long term have two options. One, invest £400 or so in comprehensive underbody wax injection and coating with a reputable company, (or DIY for sub £100 if you're up to it.

) Your car will then live longer than you, unless you are very young!
Or option two, enjoy the car until its a rusty heap in probably 12 or more years time, then scrap it and sell the battery for second life storage
But whatever, can we stop constantly moaning about rust... I bet we're putting a lot of people off buying the cars...