[RTTY] Spot frequency

[Gary AL9A]

I've read stuff about this before, but would appreciate it if someone could 
refresh my memory.  During the DLDC contest I was spotted several times by 
various stations.  Most spots were at or very near my VFO frequency. 
However, I noticed a few spots that were a couple of kHz below or above my 
VFO frequency.  For example, while running at 14082.75 (FSK) I was spotted 
at 14080.6.  Another time I was spotted 2.1 kHz above my VFO frequency.

I seem to remember this was due to the 2125 Hz shift.  Is this a difference 
between running FSK or AFSK?  In the example above was that due to the 
spotting station running AFSK on LSB?  What about the spots above my 
frequency?  AFSK on USB?  And what about the spots I send out while using 
FSK.  Are my spot frequencies correct or off too?  It was a bit annoying to 
call CQ endlessly and finally see someone spot me, but on the wrong 
frequency!  Can someone clarify this for me?

73,
Gary AL9A