Revenue on a product line the customer did not buy in the prior period. Split into new lines and returning lines. Its gap is the lines similar customers hold that this one does not, valued at their median spend.
A line bought before and dropped is a recovery, and easier than a line never bought.
Cross-sell plus upsell minus downsell is expansion. Reported as one number, it hides which of the three is happening.
Revenue in this period on a product line the customer did not buy in the prior period, per customer, split into lines never bought and lines returning after a gap.
A customer bought three lines last year and five this year. The two new lines brought $42,000. One of them it had bought two years ago and dropped, so $18,000 is a return and $24,000 is new.
Any growth at an existing customer called cross-sell. Growth on a line already bought is upsell and has different causes.