Complex Page Number Issue in Index and TOC

I'm creating a three-volume manual with eight chapters. Many of the chapters have appendices. My page numbering format is as follows:

Chapter 1-1, 1-2, 1-3

Appendix 1A-1, 1A-2, 1A-3

Appendix 1B-1, 1B-2, 1B-3

Chapter 2-1, 2-2, 2-3

Appendix 2A-1, 2A-2, 2A-3

Appendix 2B-1, 2B-2, 2B-3

In the index, the chapter page numbers are generateing correctly. In the appendix page numbers, the letters (A, B, C, etc.) are not showing up. Right now, the letters are manually typed in my footers, which I know is not right. Should I be using a variable? 

Thanks!