I have this,  My Smart Meter displayed the correct tariff when it switches from peak  rate to the night rate and vice versa.   My IHD also does the same.

Great to see a fellow Economy 7 smart meter member, @Golferbell offering you support there, @Sparkles.

I’m happy to confirm that a smart meter would be installed to match the function of your previous meter, so certainly shouldn’t mean you’ve lost your off-peak rates.

It sounds like you might be seeing some inaccurate tariff information on your new In-Home Display. As advised in this similar thread:
 

Sometimes it can take up to 6 weeks for your smart meter to complete the initialising process, which could mean that the information displayed your device might not be accurate to begin with.

Once it’s fully set-up the tariff information showing on the device should match the rates showing on the ‘Plan’ page of your online account or OVO app (download for Android or iOS). So if it’s been over 6 weeks since your smart meter was installed and things still don’t line up - reach out to our Support Team who can make sure the rates on your IHD are corrected.

Hello Golferbell - having posted my query yesterday I found out last night that the Smart Meter & the IHD do display the current correct tariff - mystery cleared & thank you for also pointing this out.