Perhaps i'm missing something, but I had the same question as above and attempted to follow your recommended solution without success. I have one sheet which contains my table, when i press the "+" button no options are given.
I was able to accomplish it when using the template supplied by numbers, but the option is not provided when using my form. What is the discriminating factor?
nope. i did it on my time tracking spreadsheet that I made form scratch. My wife has custody today (we're waiting on saving up enough for a second one now), I will try again when I get home to see when you can and connot do it.
I can't get Numbers for iPad to let me do a Form; tapping the + tab never asks whether I want a Form or a Sheet, it goes ahead & creates a blank sheet. I'm using an imported spreadsheet, not a template. If this is limited to templates, then Apple's video tutorials are very misleading.
Do you have an header row in the other table(s)? It needs that to identify what labels to place on the form.
I have found these observations while experimenting now...
A table must have at least one header row to be valid to base a form on
If that table has more than one header row, the top most one is used for the labels on the form.