Since this is a forum for game designers I thought I’d post this short question here. Background first:

I’ve had some complaints in the past with D10 games that have open-ended rolls (roll a “10,” roll again, and add the result). The main complaint is that TN 11 is the same as TN 10 (if you roll a 10 you always will add at least a “1” with your second roll).  This includes all numbers directly after a 10…so 11, 21, 31, etc. In games where TNs get pushed because of extra difficulty for extended maneuvers, there is no risk involved in pushing up the TN 1 more when you’ve reached one of these magical break-points.

The way I’ve fixed this in the past is when you roll a “0” on the D10, your next roll adds to 9, not 10.  This way the 2nd roll will add 1-9 giving a value of 10-18, with a 2nd 0 meaning "roll again and add to 18 (double 9)."  For most rolls the addition doesn’t get too bad, as people aren’t rolling a bunch of double and triple 0s.

Here’s the short question:  is there already a game out there that uses this mechanic?  I haven’t seen it before, and I'd be curious to read some reviews that talk about probabilities using a base-9 die system. 

Thank you!

is there already a game out there that uses this mechanic?

I've seen it with d10's. A Google search came up with some results that reflect this. I haven't search the forum for any yet.

You can have similar work arounds for die pool systems where each die that is equal or under a given TN is a "success".

With a TN of 11 then you simply treat the TN as 10 and then have results of 1 count as 2 successes.  With a TN of 13 results 1-3 count as 2 successes.

To get away from the automatic success of a TN of 10 (on 1d10), you can make this wrap around feature start earlier...say anything above TN 8 wraps around so that 9s and 10s are always failures.  With a TN of 13 then 1-5 would count as 2 successes, 6-8 as 1 success, and 9-0 as zero successes.

Which happens to be the system Robots & Rapiers uses.