Apple's next two iPhones had already been designed before Steve Jobs died in October 2011, according to comments apparently made by a liaison officer for the company last week.

At a meeting with the San Francisco district attorney, George Gascón, who is keen to cut phone thefts in the region, Apple's liaison officer Michael Foulkes is reported by the San Francisco Examiner to have said the designs for the next two phones "preceded Tim Cook [being chief executive]".

That would mean that both one phone due to be launched this year, as well as the iPhone 5, were already planned before Steve Jobs, Apple's co-founder, died in October 2011, just a day after the iPhone 4S was unveiled.

A passage in Jobs's biography includes him testing out the Siri voice-control function that was introduced in the iPhone that October.

But while some – including Gascón – might be surprised by the idea of a company having a two-year pipeline for the design of a phone, others who have worked in the mobile phone industry emphasised that it is not unusual.

Horace Dediu, who runs the Asymco consultancy and previously worked at Finnish phone maker Nokia, said it was not surprising. "Having worked in a phone company, I think it's a given [that the phones were designed that far back]. Work under way now is for products shipping in 2016."

Other evidence of the long design pipeline for phones comes from BlackBerry, where the new Z10 and Q10 touchscreen phones have been in progress for more than two years, with delays to the BB10 software having held up their introduction by at least a year.

Dediu added: "Software alone does not a phone make. Hardware specifications are [determined] on a different time scale."

The news disappointed Gascón, who had hoped that at his urging Apple and other phone makers would be able to co-operate on devising a common system for disabling stolen phones and tablets. By publicising it, all companies would be able to cut thefts, he hoped. But Foulkes apparently told him that researching and incorporating such systems would be "long and laborious".

In the UK, carriers already co-operate in using a common system to prevent stolen phones from rejoining the network, by identifying the IMEI (International Mobile Equipment Identity) number, which is unique to each phone. But it is not implemented internationally, so that phones stolen in one country can be re-activated in another.

Apple's work on the first iPhone apparently began in 2005, after it diverted work begun in 2003 from attempts to build a tablet device, which later became the iPad. Pictures of the early prototypes from 2005 show a large device, more like a tablet than a phone.

"Apple does not comment on rumours and speculation," a spokesperson said.