Hi Andrew, 
Thank you for using Ask Extension.

The yellowing could be caused by several things.  I would start with a simple pH test of the soil around the affected plants.  Rhododendrons are acid-loving plants and the soil pH should be 4.5-5.5.  When you start going up to 6.0 or higher, it's difficult for the plant to thrive and take up key nutrients. Here is a reference for the availability of common micronutrients based on soil pH https://www.extension.purdue.edu/extmedia/ho/ho-240-w.pdf.  If you want a more in-depth analysis there are local labs (https://al-labs-west.com/soil-analysis/ is one, but a web search can identify others) that can perform an analysis of macro- and micronutrients.  I found one old article that indicated yellow margins could be caused by a boron deficiency https://agsci.oregonstate.edu/sites/agscid7/files/horticulture/osu-nursery-greenhouse-and-christmas-trees/ond130201f.pdf.  Iron, manganese and magnesium have similar symptoms.  https://ipm.ucanr.edu/PMG/GARDEN/ENVIRON/mineraldef.html

For the notching, it's most likely root weevils but before any pesticide use, you want to positively identify the pest.  In the case of root weevils, they are active at night so getting out with a flashlight is helpful https://pnwhandbooks.org/insect/hort/landscape/hosts-pests-landscape-plants/azalea-rhododendron-root-weevil  
The pests may be active but with cold weather coming they may be less active https://pnwhandbooks.org/insect/hort/landscape/common/landscape-root-weevil