The Cass review itself acknowledges the limitations.
Also see
Steensma, T. D., McGuire, J. K., Kreukels, B. P. C., Beekman, A. J., & Cohen-Kettenis, P. T. (2013). Factors Associated With Desistence and Persistence of Childhood Gender Dysphoria: A Quantitative Follow-Up Study. Journal of the American Academy of Child & Adolescent Psychiatry, 52(6), 582–590.
https://doi.org/10.1016/j.jaac.2013.03.016
Temple Newhook, J., Pyne, J., Winters, K., Feder, S., Holmes, C., Tosh, J., Sinnott, M.-L., Jamieson, A., & Pickett, S. (2018). A critical commentary on follow-up studies and “desistance” theories about transgender and gender-nonconforming children. International Journal of Transgenderism, 19(2), 212–224.
https://doi.org/10.1080/15532739.2018.1456390
Defining Desistance: Exploring Desistance in Transgender and Gender Expansive Youth Through Systematic Literature Review (2023)
Chen, D., Berona, J., Chan, Y.-M., Ehrensaft, D., Garofalo, R., Hidalgo, M. A., Johnson, L. L., Olson, J., & Rosenthal, S. M. (2023).
Defining Desistance: Exploring Desistance in Transgender and Gender Expansive Youth Through Systematic Literature Review.
Transgender Health, 8(3), 205–213.
https://doi.org/10.1089/trgh.2021.0096