select TimestampDiff(SQL_TSI_MONTH, {d '2010-01-01'},{d '2015-01-01'}) --60 
select TimestampDiff(SQL_TSI_MONTH, {d '2010-01-01'},{d '2016-01-01'}) --73 however the diff is 72(adding extra 1 month in 6th year)
select TimestampDiff(SQL_TSI_MONTH, {d '2010-01-01'},{d '2017-01-01'}) --85 
select TimestampDiff(SQL_TSI_MONTH, {d '2010-01-01'},{d '2022-01-01'}) --146 however the dff is 144 (adding extra 2 in 12 year)

 
Year	Month	Expect	Teidd TimeStampDiff	   
5	12	60	60	   
6	12	72	73	   
10	12	120	121	   
11	12	132	133	   
12	12	144	146	   
13	12	156	158	   
14	12	168	170	   
15	12	180	182	   
16	12	192	194	   
17	12	204	206	   
18	12	216	219