Iv seen other species nest fertile eggs more then 8 months after separation, not sure but sperm retention is possible in MTD.

Sometime I use a mini mag light to candle eggs, this works very well.

The intensity and size of the mini mag is perfect, plus it doesn’t heat much.
I simply hold the light directly over the egg and see its development, blood vessels is a good indication of development.

However eggs from gravid imports are often week, especially if nesting options where poor.
If fertile you should know soon enough, sorry I cant be more specific as egg development is variable and sometimes unpredictable.

A photo would allow me to see the females overall condition but not fertility.