Good morning, Access gurus!

I'm having a brain fart and can't seem to wrap my head around the
logic for this problem, so I'm hoping someone out there can help me
out.  Here's my situation:

I have a table of debts placed by clients (we're a collection agency).
tblDebts:
DebtID (autonumber pk)
ClientID (string)
ListDate (date)
ListAmt (double)

What I need to determine is whether a debt is considered New Business
or Repeat Business.  A function that returns a boolean (e.g.
CountAsNewBiz) would be fine for my purposes.  A new client placement
is either a) a placement by a client who's never placed with us
before; or b) a placement by a client who hasn't placed a debt in over
a year.  We then have an activation period of 30 days in which we
count any placements as New Business.  Once the 30 days expires,
placements are considered Repeat Business.

Here are a few examples:
ClientID 1234A places a debt on 01/15/07 for $100.  They have never
placed with us before, so any placements listed between 01/15/07 and
02/14/07 should be considered as New Business.

ClientID 3456B places a debt on 01/15/07 for $100.  The first time
this client placed with us was 12/31/02.  They have been continuously
placing over the years, and last placed a debt on 01/12/07.  This
placement should be considered as Repeat Business.

ClientID 56789C places a debt on 01/15/07 for $100.  The first time
this client placed with us was 12/31/02.  The last time this client
placed with us was 12/31/05, so there has been a gap of over a year.
This placement should be considered New Business.

ClientID 56789C now places another debt on 01/20/07 for $150.  Since
01/15/07's placement was considered New Business and it's between
01/15/07 and 02/14/07, this debt is also considered New Business.
Anything placed after 02/14/07 would be Repeat Business.

If my explanation is unclear, please let me know.

Thanks in advance for your suggestions,
Jana