your wasting your time checking for monthly growth. too slow growing.
1) In general, from my experience of keeping tigers, the indos can grow fairly quickly(from 1 inchers), say 3-4 inches per year, up to around 6-8 inches in total size.
2) Then after, they will slow down anything from 1/2 to 1 inch per year.
3) Then roughly after 11 inch, growth rate slows down EVEN more. lucky to have 1/2 inch per year.
4) At this point in their life, they start to bulk out, growing deeper and thicker noticably, rather than just length.
NGT and NTT have quite sluggish growth rate compared to Indos (growing only say 2 inch per year when small, again slowing down at about 6 inch)
ST's.... similar to Indo, exept they get bigger when fully matured.
Convert a tiger on to pellets however will increase the growth rate noticably, say after 1 year. Big tank, good water q, good filtration and good quality foods will also help.