"..... It is poor organisation on their part to leave you with the whole weekend to think about it: my friend only got told the day before she needed to go back, so had much less time to worry. (Equally, though, that made her think it was urgent...)"
You have made your own point. The NHS cannot win, can it?
That they can't rush you back in immediately there's the slightest discrepancy, they're 'poorly organised'. The minute they have an immediate turn around service, they're causing unnecessary anxiety.
What do you want, AmINearlyThereYet? bearing in mind any immediate, instantaneous service costs ££. The NHS are in the business of healthcare for everyone. Sometimes a weekend's anxiety is the downside of trying to help everyone.
As for the OP- really, there are many reasons why the recall. Your boobs are 3D structures, the mammogram is a 2D structure. Superimposition occurs. The screening service aims to get as many women through as is safe in a given clinic, and this invariably means that the cursory glance-over the radiographer has time to give your images (checking, really, for technical quality, not diagnosis) may miss something subtle. The images are then, a bit later, reviewed by someone whose sole job it is to read the images. They may then call you back for images at different angles to separate 2 overlying structures out. This is by far the most efficient way of handling mass screening. Of course, I cannot lie, those images may reveal that there is a cause for concern- BUT, and this is a biggie, if it wasn't see on the initial images, or recognised as being 'a worry' then, if (IF, IF) there is a tumour, it's going to be very small, very early and thus highly treatable.
FWIW, mammography is actually a highly skilled art. Those women are senior radiographers. They know having an mammogram is both routine, potentially scary and hurts! And there is no doubt about it (and I am speaking GENERALLY here!!) some women compromise their mammogram by not cooperating to the extent that they might otherwise be capable. This can require a recall, too- slightly blurry images because the patient moved during the exposure. I am by no means accusing the OP but that's another reason why women get recalled.
Can you tell I've done some mammography in the past!?
Best wishes, OP!