Let’s follow the current derivation:

A1  
⇒ A2  
⇒ A3  
⇒ 10 A15  
⇒ 10 A16 A13 A4 A12  

– A16 ⇒ 12 A8 ⇒ 12 A9 A10 ⇒ 12 7 A10 ⇒ 12 7 3 A11 ⇒ 12 7 3 1  
– A13 ⇒ 9 A14 ⇒ 9 2  
– A4 ⇒ A5 A6 ⇒ 5 A6 ⇒ 5 4 A7 ⇒ 5 4 6  
– A12 ⇒ 8  

Putting it all together gives:  
10, 12, 7, 3, 1, 9, 2, 5, 4, 6, 8  

We need one more terminal “11” at the end.  The simplest way is to insert “11” into the A12 rule, so that A12 produces “8 11” instead of just “8.”  That is a single insertion, and it yields exactly the target sequence.

Updated production rules:  
rule_13: A12 -> 8 11