secure erase: wifi password retained ?

Hi,

Sorry for the lengthy post :-)

I want to return my 2014 macbook pro with mavericks to my previous company wiped perfectly clean.

2 "problems" :

1/ erasing the partition

After booting with "cmd + r" and "secure erasing x7" the correct partition of the SSD, i wanted to install a fresh copy of mavericks from my recovery partition.

I rebooted and again pressed "cmd + r" and it started "internet recovery" automatically (thus remembering my wifi credentials ... scary !!!)

After some googling i found that "cmd + option + p + r" wiped some memory and indeed, it now asks to which network i want to connect after i boot with "cmd + r" (instead of "remembering" the wifi network)

Questions :

- how can i make sure NO more data is retained ?

- can other data still be recovered after this 7 pass secure erase ?

- how can i access my restore partition and install os mavericks from there instead of downloading it from the internet?

2/ unlink between apple id and macbook

I suspect that there is some kind of link between my apple id and the machine, itunes, icloud, i-dontknowwhat, etc etc

What i want to avoid is that, because of this link, some cloud-data (that is linked to the macbook) is synced back once the new owner is using it...

How can i make absolutely sure that this is not the case ?

A few weeks back, i already logged in with all my apple id's @ htpp://supportprofile.apple.com and one of the logins indeed showed a link to this machine.

I pressed the "unlink" button, but this unlinking had to be confirmed through a mailbox that i do not have access to anymore...

Yesterday, if i logged in again at the same website, the machine is not linked anymore (so without confirming the unlink !)...weird ?

Question :

- how did the unlink happen and how can i make sure that there is no link anymore ?

ps : yes, i have already read this guide What to do before selling or giving away your Mac - Apple Support.

kind regards and thank you,

Tom.