Yet another little polish for that issue:
Now I get sales invoices nicely collected, thanks to sale invoice grouping module.
Could I configure my invoice template in a manner so it inserts a line above any single order saying “your order of date :” ? - Sure, can be done by hand - but hey, we’re lazy, aren’t we? (at least I am)
I guess you will have to loop over the lines grouped by origin and insert a line per origin.
The groupby is not available in the standard report context so you will have to extend it.