I have heard contradicting things on whether warranty is based on Serial Number (Date of Batch Manufacture) or Date of Invoice.
I have read(dont remember where) that distributors (when they buy a batch) are duty bound to sell that batch within a certain span of time, else return the stuff.
Which is why most service centers only care about the serial number. From the serial number they know whether a product is under warranty or not.
I'll give you an example. Consider a product that was manufactured on 1 Jan 2000 with serial number SN01. When the product is manufactured the vendor assumes that the product will be sold off in the next say 3 years maximum and the product has a warranty of 3 years more. So they will input in their system a Warranty for prodcut SN01 uptil 31 Jan 2006.
Now, the distributor sells this after 1 Jan 2003 - then theres a grey area. Some manufacturers will allow that, while some will not. They have a reason to do that. Lot of times ( and i know some people who are guilty of this) will buy a electronic product without a bill from a friends shop. And after a year if the theelectorincs product fails, they will go their vendor and ask for a 'current' bill with a date much later than the product was sold at. That way, manufactueres found that lot of the old stock which should have been out of warranty - was ending up at thier RMA centers for service.
To counter this strategy, the manufactueres now use the Serail Number to address warranty issues.
So effectively, when you are so happy that you bought the product from flipkart with a nice looking invoice and VAT paid bill - it means nought

Flipkart has been accused before of selling illegally acquired goods, where manufacturers have refused to honor warranty based on bill because they did not sanction that batch of products to be sold in India, let alone flipkart
