Was looking at some of my Scott 723 Street Definitives and noticed there are what looks like 2 different print qualities..
Here are the 2 stamps side by side, left one being in poor quality and the right one being of higher quality.

Below is a different look at the 50 cent denomination..You can see the colour difference.

As you can see by my colour annalist program, the left stamp leans towards the ORANGE spectrum of the colour scale while the right stamp leans towards the VIOLET scale.

Te SKY also has colour differences..Te left stamp contains a YELLOW tinge while the right stamp leans towards an ORANGE tinge as shown below.

The building itself...The LEFT stamp itself shown un uniform consistency of poor hatching in the design, while the RIGHT stamp has uniform hatching.

The car has the same poor/goo hatching affect as shown below..


Now this could be caused by a lot of things..
1- Burned different plate as the run proceeded..
2- Cleaning the machine after a days run and re-inked the next day
3- OTHER reasons.