Two possibilities come to mind:

1) If the tops of the plants were more exposed to cold, winter sun, and wind, then the buds on top may not have been protected as much as those on the side. In this case you will have dead buds on top.

2) If you pruned the top after mid summer, you removed the flower buds since they are formed by mid summer. In this case there will be no buds on top.

I noticed your other post, but I'll answer again. A picture would help. Without seeing it, I think you are right in suspecting winter kill.

(Anything clearly dead should be removed with sharp pruners so as not to offer a foothold for secondary disease and insect problems)

Thank you both for your replies. How do I post a picture? I tried to look for information on it but could not find any. I did cut off the top last year and a strange winter. When should you trim it if it needs it? Thanks again.

Since rhododendron and azalea plants start forming new buds shortly after blooming, there is a small window of opportunity after they bloom. If you prune within two weeks after blooming you are safe. You could probably get away with pruning up until the beginning of summer without loosing any buds and maybe up until mid summer and only loose some buds.

This summer watch your plants and follow to see when they form their buds. You may not be able to tell the difference between flower buds and leaf buds that early. When the flower buds begin to swell up in the fall or late winter, they become more obviously different.

Many spring flowering shrubs need to be pruned right after they bloom to prevent loss of flowers for the next year, as they bloom on the previous seasonÂs old growth. Spring flowering shrubs that may be pruned once bloom is completed include lilac, Pieris, Daphne, azalea, rhododendron, Spirea, forsythia, spring flowering viburnum, weigela, flowering quince, red-twigged dogwood and deutzia.

Here is a link that might be useful: Pruning spring flowering shrubs