I read an email that states launching Witcher 3 through the GOG app - will leave a letter and armor in Vizima without upgrading to Nex-Gen but all I receive is an egg receipt in both a new game and a new game plus.

Anyone else having this issue?

The weapon and armor set was added to the next-gen update. "Any version" and similar refers to the fact that it also applies to the base game, not just the Complete Edition, on any supported platform or storefront.

"But besides all the amazing improvements that this update has brought to CDPR’s masterpiece (full list of changes HERE), there are also awesome in-game rewards waiting for you to redeem, like brand new gear for Geralt, which you can put to use on your monster-slaying adventures throughout the Continent!"
-- Complete Edition in-game rewards announcement thread

Also of interest:
"Do I have to start a new game to claim my rewards?
No, you can claim your rewards at any time, regardless of how far you’ve progressed into The Witcher 3: Wild Hunt. If you begin a new game, please note that your rewards will be waiting for you in the Royal Palace in Vizima, which you will reach through the main quest.

Do I have to be connected to the internet in order to participate in MY REWARDS?
An internet connection is required to register with The Witcher 3: Wild Hunt MY REWARDS. Once claimed, rewards will be yours to keep regardless of whether you’re playing online or offline. Please note that if you begin a new game, you will need to log in again to obtain the rewards in that save file."

-- My rewards - official Witcher site