Very good again..presumably you are adding 3 clues .... what inspired it was this .. from

What is most solved cells with "n" clues?- Code: Select all
`+---+---+---+`

|...|3.1|...|

|2.4|...|...|

|...|...|...|

+---+---+---+

|8..|52.|...|

|...|...|9.1|

|...|...|3..|

+---+---+---+

|...|.4.|.5.|

|91.|...|...|

|.3.|...|...|

+---+---+---+ this 15C found by G Royle has only 576 sol

solves to

+---+---+---+

|5.9|3.1|...|

|2.4|.95|13.|

|1.3|...|59.|

+---+---+---+

|891|523|...|

|35.|...|9.1|

|.4.|91.|3.5|

+---+---+---+

|.2.|149|.53|

|915|.3.|...|

|43.|.5.|.19|

+---+---+---+ which has 29 more solved clues ! [still 576 sol]

Adding 2 clues does not give a 17C

Adding 3 clues gives us 1093 minimal 18C - although many from the same grid solution

and this 15 clue [one clue different] has 2715 grid solutions

- Code: Select all
`+---+---+---+`

|...|3.1|...|

|2.4|...|...|

|...|...|...|

+---+---+---+

|8..|52.|...|

|...|...|9.1|

|...|...|3..|

+---+---+---+

|...|.4.|.5.|

|71.|...|...|

|.3.|...|...|

+---+---+---+

Adding 2 clues gives one 17C [ thats how Gordon found it, I suppose]

Adding 3 clues gives us 1150 minimal 18C - which are different but again probably many from the same grid solution

I admit that it is highly likely that all these solution grids are known, and presumably remote 18C wont necessarily have a 15C subpuzzle with a low sol count / extra solved clues ....