By my calculations, 2006 would have had $3059 (or $3054*) of depreciation

Starting in 2007 it would be $3187 per year.

So in 2018, the "prior depreciation" would be $38,116 (or $38,111*).

In 2019, the "prior depreciation" would be $41,303 (or $41,298*).

How does that match with things?

Keep in mind that if the business percentage varied or if they ever used the Simplified Home Office deduction, those numbers would be different.