Client contributed $17,500 when established C-corp.  On year 2, C-corp changed to S-corp with  negative retained earnings of $4200.  So, client's cost basis was still $17,500 when changed to S-corp.  Negative AAA of $4200 was recorded in S-corp balance sheet (with $13,300 bank balance to start with S-corp activities).  During the years, client contributed additional $1500.  

At end of 2024 before company dissolved, with 2024 net losses, his basis = $4435.  Less $235 distribution received, basis = $4200.