Im using lumia 620 since the first day of launch in malaysia.. At the beginning i had push notification issues.. But it was solvespd after lumia black updatw. Now with lumia cyan/8.1, notification centre very up to date together with push notification. After this if any push norification issue, i would blame the app developer. Bcoz my whatsapp,facebook,instagram beta all very quick notification i woukd say.