How an A-page gets created
Say scene 18 starts halfway down page 23 and runs to the bottom. The blue revisions add eleven lines of dialogue to it. Page 23 can't hold them, and the script is locked, so page 24 can't move. The fix:
| Before (white) | After (blue) |
|---|---|
| Page 23: end of sc. 17, sc. 18 | Page 23 (blue): end of sc. 17, first part of sc. 18 |
| Page 24: sc. 19 | Page 23A (blue): rest of sc. 18, then white space |
| Page 24 (white, unchanged): sc. 19 |
Page 23A will often be mostly blank. That's fine and expected. The empty space is what keeps scene 19 on page 24 for everyone who wrote notes on it.
If a later revision grows scene 18 again, the next overflow page is 23B.
The opposite case: combined pages
When a revision cuts material, the leftover space is handled with a combined page number. Scenes 20 and 21 on pages 26 and 27 get trimmed so both fit on one page. That page is numbered "26-27" and nothing after it moves. Printed scripts sometimes show it as "26 - 27." or "26/27."
Why it matters for breakdown and schedule
Nobody schedules by page number, but everyone communicates with it. The script supervisor keeps the lined script by page, department heads circle things on pages, and a note that says "check the lamp on p. 24" needs to point at the same lamp in November.
What does need updating is scene length. A page runs about 54 lines, so eleven lines is close to 2/8. If scene 18 was 6/8, it's now a full page. The page eighths on the breakdown sheet and strip have to be re-measured, and the day's page total on the schedule changes with it. The page count calculator can help with the arithmetic.
Common confusion
A-pages and A-scenes get mixed up constantly because both use a letter suffix. They are independent. The eleven new lines above created page 23A but no new scene. A new two-line scene inserted after scene 18 would be scene 18A, and if it fit on page 23A, you'd have scene 18A on page 23A. The revision colors page shows what the header and margin asterisks look like on these pages.