I've sorted it out by passing the variable through the ProductController.php

at $this->ajaxRender(Tools::jsonEncode([

I added: 'ps_last_qties' => Configuration::get('PS_LAST_QTIES')

and then I received it at core.js: o.default.on("updatedProduct", function (e) {

and was able to use it as e.ps_last_qties