It is better to follow GSTR-2B because there is better control in the long run but if you want to take itc as per Gstr-2A then also it is valid but make proper reconciliations
If itc is showing in Gstr-2A but not in GSTR-2B that means the suppler has filed his return late. It will show those invoices in GSTR-2B of next month. Therefore you can avail those itc in next month GSTR-3B