Yes, if you have a Z1 and an MX60, those devices have model-specific licensing as well as different costs, and their combined value will determine the new co-termination date for that Dashboard Organization. You can use the licensing calculator to simulate this here: https://dashboard.meraki.com/manage/dashboard/license_calculator where you can put in any combination of licenses and see approximately where you'll be.
Also, when you make the purchase, you'll typically get an order number and/or a license key in your email. Typically if yu have an order number (like buying new equipment) you would use the "Claim" button on the Organization > Inventory page, and if you have a license key you typically go to Organization > License Info and select the Add License link. Be careful with the operation dropdown, if these are the only 2 devices in that Org, you'd be using the "Renew my Dashboard license" operation, as opposed to adding more devices. Regardless, Dashboard will show you the before and after licensing state before you apply it, in case there are any warnings.
Rather than renewing the MX60 licence I would seriously consider replacing the hardware with something more modern.
I particularly like the MX65. It has 10 Gigabit LAN ports (so small sites often don't need a switch), and two of the LAN ports are PoE (so you can use them to power an access point or a VoIP phone for example).
Both the MX64 and MX65 are going to be a lot faster than an MX60. So you might be able to use a faster Internet circuit in the future.
Also note the "End of Support" date for the MX60 is October 24th, 2022. So you have a maximum of 4 and a bit years left.
Thanks for your help, much appreciated and clears things up.
I'm aware of the 2 options when renewing / adding licence, from having a test MR33 - i'll be sure to select 'update'.
We are waiting on a quote from Cisco for renewal.
I appreciate that the MX60 isin't a rocket by today's standards (mainly 100Mbps WAN), but it'll do for another year.
I'm curious as regards to end-of-life. When the MX60 reaches EOL, what happens it? When the licence expires, does it just die or what? Seems like a bit of a con to me.... after buying the hardware / licence for X years, does the device just become redundant?