This can be somewhat normal for container-grown citrus, but check the leaf undersides and young stems for signs of pests if you haven't already. Look for scale, mealybug, spider mites and whitefly, all of which tend to cluster near the main vein on the leaf underside or where the leaf body meets the leaf stem; their feeding can sometimes cause patchy discoloration. Otherwise, it may be have been a bit nutrient-deficient this past growing season, or the roots may have been kept a bit too wet, which impedes their ability to absorb the nutrients they need even if levels in the soil are sufficient. At this point, plants coming indoors should not be fertilized as new growth should not be encouraged (since indoor conditions are not optimal for growth), but you may need to resume fertilization in spring when it goes back outdoors.

Neem oil, even when useful for pest control, will not reverse the damage done by those pests. Leaf tissues that are discolored or injured do not heal or regain a normal, even coloration, though when new leaves emerge, they should look better if the problem has been corrected. Similarly, once a stress factor initiates the process of leaf drop ("senescence"), a correction to the problem will not halt the shedding of leaves already in-progress.

This page gives more information about the care of citrus when indoors, though you may already be aware of it given the older plant that you had previously: https://extension.umd.edu/hgic/topics/growing-dwarf-citrus

Miri

Thank you so much! Fingers crossed.

Our pleasure.