If order matters and it may come from many sources (replicas), then one
solution is to use a dateTime field as your order code. It will not be
incremented, but you get a known order (assuming no one tampers with the
clock). If there is a risk of two records being created on the same
second, you can use the Timer() function to get ticks down to below
Another solution is to give each replica a Prefix. Increment a counter in
the replica and generate a String Key of PrefixNumber. Within each
replicas sources, you will have an incrementing counter, but different lists
for each replica. Kind of like several books of receipts: each book is
sequential, but there is no order between the books.
Let us know what you decide.