A yellow tile with two small stations can be upgraded to any green tile with one station and the same exits. #69 is special.
1	55	14	888	2	56	15	887
69	119
A yellow tile with one small station can be upgraded to any green tile with one station.
3	12	14	15	887	888	119
58	12	13	14	15	887	888	119
4	14	15	87	88	119
A yellow tile with one large station can be upgraded to any green tile with one large station.
5	12	14	15	119
6	115	12	13	14	15	119
Below here there is no neat summary rule.
B	12	13	38
10	35	36	37	38	64	65
52	64	65	66	67	68