I'd have a couple questions about this progression for you. First, is the 13th measure just going back to one, or is it really a 13 bar progression? Rewriting it with bars helps. Second, does the 12th bar really have 5 chords, or is there a typo?
| G | C7 | G | G Db9 | C9 | C9 | G7 | G7 | G/A | D G/D D | G C |
G/F Eb9 D9 Ab9 G13 | G13 |
First off, not all blues progressions are 12 bar blues. There are 8 bar progressions and multiples of 8 and 12.
Second, there is a basic (very simple) template for the 12 bar blues that is greatly embellished by jazz and blues artists. Sometimes it is so embellished it is hard to find the patterns other than counting 12 bars. In it simplest form one has (in G):
| G | G | G | G | C | C | G | G | D | C | G | D |
The "land marks" for lack of a better term are indicated below (this is somewhat subjective).
| G | - | - | - | C | - | G | - | - | - | - | D |
Staring on any chord we expect a jump to the IV at measure 5, and back to I in measure 7. After that there has to be a "turn around" in the last measure that "USUALLY" ends on the V (V7) to resolve back to I. Dominant 7th chords (or an extension) are almost always used for each chord. Most players expect a jump to V at measure 9 but this is not a hard and fast rule. In the dashed measures people often throw in cycle extensions and substitutions to the point of no return. But if you understand these cycles you can decipher the basic pattern and see the logic. Some players put Rhythm Changes in after the I in measure 7. One of the more common embellishments is to jump to the IV i measure 2 (called a fast 4), which yours has. Wes Montgomery jumps to the flat 7 in measure 2 in West Coast Blues. The Db9 is really just a substitute for the G7. I can't explain the 13th bar, but I once wrote a blues tune with 11 bars to create a particular feeling. The bunch of chords in the measure before looks like a turn around with substitutions. You might want to check out the following tunes. imo these are really 12 bar blues in disguise, some more disguised than others.
West Coast Blues
Blues for Alice
Good Bye Pork Pie Hat
Again, some of the changes are really stretching the template but it's in there. Chord substitutions and cycle extensions are a big part of the formula. But the blues has such a distinct feeling that you could stay on the G blues scale over the changes and develop a good solo (at least for starters).