T-SQL (SS2K8) :: Repopulating A Sequenced Column That Has Gone Out Of Sequence

We have an application which has had a big design floor and is now causing an issue which needs to be rectified. It inserted data in batches of 2000 rows which should have always been in sequence. A column was used which recorded an ever increasing numerical value for each row that was inserted. So batch 1 would have a start value of 1 and an end value of 2001. Batch 2 would have a start value of 2002 and an end value of 4002 etc.

The problem is the application which inserted these records in order, missed some records. So in actual fact we have:

Batch 1 = seq 1 - 2001 (total 2000)
Batch 2 = seq 2002 - 3998 (total 1996, 4 missing)
batch 3 = seq 3999 - 5999 (total 2000)

Now the missing data has been found, it will be inserted at the end of the table, as we cannot insert it where its should be as the sequence value has been used by the next batch already. Lets say the table is 10,000 rows so far, so the seq for batch 2, for example, will be 2002-3998, then after the missing data is inserted, 10,001 - 10,005. The application uses these sequences to show the range of data so where it should be 2000 rows being returned, it would now show 8003 rows - all the other batches between the first and last sequences for the batch!

I need to change the sequence values across the whole table so they are in order. I can select the data in the correct sort order as there is another unique key on the table, but unsure how best to use this to change the sequence column to be in order for all rows. Adding an identity column would work and then remove and rename the seq column, but I obviously cannot add this based on another columns sort order. The identity column would use the clustered key which is in the incorrect order!!