It doesn't add up, hence my question.
Here, the Grocer gives 4 (base) +3 (Expansionist Attribute Point) +8 (Improvements) = 15 -> nothing for uncultivated rural tiles, while there are a lot of them.
View attachment 721027
There, the Grocer gives 4 (base) +3 (Expansionist Attribute Point) +8 (Improvements) = 15 -> +3 for uncultivated rural tiles, while the only ones left are for Woodcutters and Mines (the orange is for tiles of neighboring settlements).
View attachment 721028
First, Hastings.
With the listed Improvements, the Grocer gives 4 (base) +3 (Expansionist Attribute Point) +9 (Improvements) = 16, so now (with one more Farm and one more unimproved Flat Plains Wet tile), it gives 1 more point at 17.
After purchasing it...
The Fishing Boat on the Reef doesn't get the bonus (I've tested on another Settlement with more Coastal Fishing Boat, and that's definitively the differiencing factor for Fishing Boats), and the Coffee Plantation, the Tobacco Plantation and the new Farm get +2 (the three are Improvements gained during the age transition because of the appearance of the new Resources, and the Farm that I've added myself). The Farm with Science was a Gypsum Mine in the previous era, there might be a bug with the yields here.
Fun fact, -1 +3 does not add up to the +1 that I was trying to explain, but is actually +2...
We can also see +1 Food on all unimproved tiles, but these yields are still unimproved, unworked and not gained, and the actual Woodcutter and Mine have no more Food than without the Grocer.
So, now Ostia.
(Why did I choose a Settlement with so add borders as an example?)
With the listed Improvements, the Grocer gives 4 (base) +3 (Expansionist Attribute Point) +8 (Improvements) = 15 -> it still gives 3 more point at 18 (this Settlement has not changed since last post).
After purchasing it...
There are Reef again under the Fishing Boat in the Lake, and its Food has not changed. But all 4 Farms have got +2, and only one of them (south-west of the Town Hall) is new in this age. -1 +4 = here we have the +3 I was searching for.
Last one, Colcestre.
Colcestre gained the Orange Plantation with the new age, and has since expanded all the way to the Gold (Mine, Woodcutter, Gold Mine).
6 Improvements boosted by the Gorcer, +4 (base) + 3 (Expansionist) = 13 vs the 15 announced.
And... we got once more time one more point than announced, with all the new tiles except the Gold Mine gaining one more than expected.
Here we can see that the unimproved Reef doesn't get +1 either.