pagination of keys in tactile supplement

Tactile supplements are dealt with in section 9 of Guidelines and Standards for Tactile Graphics. I am trying to get a better understanding of your description. Did you mean that there are 3 graphics on the print page, or that in print there is one graphic that you have split into 3 parts.
If you are dealing with this latter situation, and each of the keys (for tactiles 1 and 3) are [u]not[/u] more than 1 page each, the print page number that appears on the top right corncer would be 655, a655, b655, c655, and d655 as you indicated in your question. The braille pages are numbered sequentially within the supplement volume (see 9.8.2 of the Guidelines), beginning with #1. The key pages would be punched on their right side and bound as facing pages with the print and braille page numbers still placed at the top and bottom right side of the page. The tactile supplement braille pages do [u]not[/u] have a preliminary identifier such as "l" for Legend. The supplement volume would have "t" pages, and "p" pages (as preliminary pages similar to any other braille transcription). In addition to the Special Symbols page, there may be a Graphic Symbols page (see 9.7.3 of the Guideliines)which would contain symbols that are used consistently throughout the supplement, rather than repeating them for each key.

Note that the attribution, reference and source information should [u]not[/u] be included with the tactile graphic, but should be placed after the figure number or diagram heading in the braille volume (9.5.1). However, illustration caption and figure descriptions [u]should[/u] accompany the diagrams in the supplement so that the reader can interprt the tactiles without having to refer back to the braille volume (or e-text, or audio). The caption and description [u]should also[/u] appear in the braille vollume (or e-text, or audio) for readers that want the information contained within the caption, but may not be using the tactile supplement.

Note also that if any of the key pages are contiinued onto a second page, then the format for numbering and binding is changed so that the graphic appears on the left side (of an open volume). All of these key pages are punched on the left side and bound following the graphic as pages facing the graphic page. (See this exception stated in 5.8.3.3 of the Guidelines Section 5.12 deals with the page numbering of interpoint braille volumes which is generally not used for supplementary diagram volumes.
Hope this answers your question!

Betty