Final payment and memo lines in checks

I am a GC on North Carolina. I recently invoiced a client for Final payment. The client sent me a check for 25% of the amount due per contract. Written in the memo line were 3 letters. "Bal". if I accept and deposit the check does that constitute Final Payment or Paid In Full? There was an original contract based on a definitive Scope Of Services that was signed by the client and myself. As they project progressed the client added many change orders to the project.. The check they sent ONLY paid the balance on the original contract. They omitted the change orders that they were invoiced for. Since the change orders were not included in the original contract can it be treated as two separate projects.? Therefore enabling me to collect on the change orders. Thank you