[AccessD] A2K:Loop Syntax for Update SQL

Hello all
When I create a record in an app I am making
I record a combination Alpha/Numeric code (stored
as Text)
Something like ABC:123. The next booking would be
recorded
as ABC:124 then ABC:125 etc etc
(The ABC bit is constant, because it's our Company
initials)

We also allow for block bookings (recurring
bookings really) based on the details
for ABC:123 to occur also.

What I want to do is once the original booking
details for ABC:123 has been made
If someone wants to make a recurring booking based
on ABC:123, I want
all the recurring bookings to get the same
Alphanumeric number (This bit I can do) but
my real problem is I want to append stuff to the
end of each AlphaNumeric in the group

EG the first booking for a recurring booking based
on ABC:123 booking will be ABC:123-1 the second
ABC:123-2
the 3rd ABC:123-3 and so on and so on

Any suggestions?

Many thanks in advance

Darren