I suppose you have some auto-generator for unique 16-char codes.

Let's say it's encapsulated in function dbo.GenerateUnique16key.

Then you should have something like this:

Create TABLE dbo.AccountIdentifiers (

TwentyTwo char(22) NOT NULL PRIMARY KEY,

Sixteen char(16) NOT NULL DEFAULT (dbo.GenerateUnique16key)

)

When new records arrive insert 22-char codes into this table.

Table will generate 16-chars unique codes and assign them to imported 22 char codes.

Then mapping (converting) will be easy once and forever.