The solution was provided by re-arranging the <sup> tags to enclose the <a href . . . >
Doing so did solve the problem with links with Kindle to PC 2 reader and Kindlegen Previewer.
It took awhile for me to complete the corrections but I hope a heads-up warns others with endnotes or other <sup> + <a> tags strings will be alerted to the solution with Kindle conversion loss of hyperlinks within text or external sites.