What is the significance of persistently elevated lymphocyte levels (2 years, slightly above the normal range)?

Could be serious: Please have your doctor check this out. There is a condition called cll, which causes the lymphocytes to be elevated. If you are middle aged your risk for this is increased. It is a slowly progressive form of leukemia, but with monitoring, you can do well. If that isn't it, you may just have more lymphocytes than is "normal".

Increased WBC: Increased WBC can be caused by several things. It could be mainly a reactive process to certain infections/inflammation/or malignancy vs other primary bone marrow problems. If the elevation of WBC becomes persistent- ( you mentioned- the WBC has elevated for 2 years) -; it really needs to be investigated further for primary bone marrow disorder. Please see a hematologist.