Account References - Sage Link

[Spitos]

Our account references are made up of the first 4 letters of the customers surname followed by a / and then three numbers which run in sequence from 000 to 999.
For example, the first ever 'Smith' to order will have this reference:
SMIT/001
Then it would be
SMIT/002
SMIT/003
SMIT/004 etc etc.

We have now reached SMIT/999 and are having problems importing new customers into sage.

We have tried deleting the following account references in the hope that new customers will be assigned a reference starting from the next free number available:
SMIT/001
SMIT/002
SMIT/003
SMIT/004
SMIT/005
SMIT/006
SMIT/007
SMIT/008
SMIT/009
SMIT/010

But when we try to import the new account details, we receive a message:
"No sequence numbers left"

The account is imported with this reference:
!BPPLA01
But also with the address details of what was formerly SMIT/001.

What can we do to remedy this so that the format is still the same for new customers if the number sequence is maxed out?
We want to avoid changing the way that the references are generated in order to keep uniformity between all accounts.