NC 25 a long time ago 1929 Official

NC 25 becomes NC 75 1935 Gen Draft

About 1956 or 1957, NC 75 was extended east a couple blocks over what had been part of US 74-A to end at NC 200 which was using Main St at the time.
By 1962, NC 75 was extended along a rerouted NC 200 out Hayne St to US 74-601.

NC 75 initial Monroe end 1936 Union County

NC 75 extended to NC 200 1975 Union County

NC 75 extended out to US 74-601 1962 Union County

In December 1978 (NCDOT), NC 75 was truncated back to Franklin/Charlotte intersection in Monroe.
In August 2011 (NCDOT), NC 75 was supposed to have been extended north on Charlotte St and east on Church St, replacing NC 200 to NC 207. However, it appears what happened instead is that NC 75 east was truncated back to the newly designated NC 200 along Martin Luther King Jr Blvd west of Monroe. Franklin St is now SR 2100; Charlotte St is SR 1009; Church St is SR 3521.

NC 75 truncated to NC 200 Charlotte St 1982 Union County

NC 75 truncated to NC 200 west of Monroe 2017 Union County

The first NC 75 was an original state highway that ran from NC 18 (or possibly at NC 17-18 jct) Lenoir through Taylorsville, Statesville, Mocksville, Lexington, Asheboro and Siler City to Pittsboro, then north through Chapel Hill to Durham, then northeast to Oxford before heading into Virginia below Clarksville.
In June 1924 (NCDOT annual reports), NC 75 was removed from bits of SR 1507 Wilson Town Rd Stovall and SR 1445 Buckhorn Rd Bullock, plus a lengthy abandoned segment east (but not immediately adjacent) of the railroad in between.
In 1925, NC 75 was rerouted at Mocksville to follow NC 26 (current US 21) north to Turnersburg, using what I guess is Mount Bethel Rd and Rimrock Rd over to NC 901. The old route used US 64 Davie Ave; SR 2437 Wilson Park Rd and SR 2158 Old Mocksville Rd.
In 1926, NC 75 was changed to leave NC 26 at Dunlap, using Dunlap Gate Rd to Old Mocksville Rd over to NC 901.

NC 75 no NC 26 duplex 1923 Auto Trails

NC 75 follows NC 26 1925 Official

NC 75 adjusted again 1926 Official

Also about 1926 (per NCDOT annual reports, though shown starting with the 1924 Official Map), NC 75 was rerouted between Durham and Oxford on a brand new road via Creedmoor. The old route remained NC 13 (now US 501 Bus) north to Braggtown; used SR 1004 Old Oxford Rd to Oxford, utilizing Hillsboro St (except: a substantial abandoned segment to the west from about the Little River to Tenaka Pkwy; Old Flat River Bridge and the SR SR 1774 access road; abandoned segment from FCI-2 Butner entrance through the center of FCI-1 to about where the development center is; in Stem it used SR 1132 W Talley Ho Rd and the fully removed Church St which was just past Main St; SR 1136 Tally Ho Rd, SR 1138 Culbreth Rd, abandoned routing, Mabel Ln, abandoned routing; abandoned routing/SR 1168 Hallie Burnette Rd)

NC 75 avoids Creedmoor 1922 Auto Trails

NC 75 embraces Creedmoor 1924 Official

In December 1926, US 15 was assigned to NC 75 from Pittsboro to the Virginia line. Additionally, NC 75 was rerouted at Pittsboro to follow US 15 south to Sanford (replacing NC 53); duplex with US 1/NC 50; replacing NC 74 to Carthage; replace NC 702 to Pinehurst; duplex with US 311/NC 70 to West End; replace NC 512 to Ellerbe; replace NC 51 to US 15's south end at US 1-74/NC 20-50 (now Hancock at Washington) Rockingham. The former NC 75 from Pittsboro out to Lenoir was renumbered as NC 90. That route used by NC 75 is US 64 except the following (from Lenoir): Harper Ave; SR 1565 Lower Creek Dr and a bit of SR 1564 Taylorsville Rd; SR 1789 Log Cabin Pl and SR 1348 Old NC 90 between Lenoir and Taylorsville; Front St west of Newton Dr in Statesville; Wilkesboro St, Salisbury St, Depot St. through Mocksville; SR 1602 Juhn Crotts Rd; SR 1605 Garwood Rd/abandoned/Sheridan Ln/most of SR 1694 Hawthorne Rd; most of SR 1607 Aubrey Merrel Rd; SR 1611 Fork Bixby Rd, SR 1612 Fulton Rd, NC 801, abandoned Fulton Ferry across the Yadkin River; unmarked gravel road and SR 1194 Yadkin College Rd through Yadkin College
NC 75 used SR 1192 Old US 64 east of Yadkin River to Lexington (except around the NC 150 area - NC 75 used abandoned route north of SR 1192 and crossed NC 150 south of Reeds Baptist Church Rd); SR 1192 becomes 5th Ave; Main St then E Center St out of Lexington; SR 2205 Raleigh Rd/SR 1344 Old Hwy 64, except NC 75 used SR 2259 Old Hwy 75 east of Lexington; SR 2273 Valley Mine Rd to Cid; SR 2416 Old Hwy 109, SR 2318 Cid Rd and SR 2270 Jarrell Rd back to Pleasant Grove; SR 1390 Gallimore Town Rd; SR 1335 Rush Mtn Rd; abandoed bridge over Uhwarrie River; SR 1382 Tabernacle School Rd; SR 1333 Robbins Cir/Old Road Dr; SR 1416/1004 Old Lexington Rd which becomes Salisbury St in Asheboro; NC 42/SR 2237 on Salisbury St (except used Martin Luther King Dr); US 64 Business east of Asheboro and SR 2713 Trogdon Hill Rd; SR 2235 Andrew Hunter Rd to Franklinville and NC 22 to Ramseur; SR 1169 Graham Moore Rd, SR 1370 Benjie Williams Rd, SR 1107 3rd St through Siler City; SR 1503 Stage Coach Rd, SR 2234 Stage Coach Trail, SR 1503 Harold Hart Rd, lengthy abandoned loops, a bit of SR 1506 Pleasant Hill Church Rd, more lengthy abandoned loops, Harlands Creek Dr, SR 1648 Wagon Trace, SR 1564 Old Siler City Rd; US 64 Business to Pittsboro.

Hodgepodge from Pittsboro to Rockingham 1926 Official

NC 75 rerouted Pittsboro to Rockingham 1930 Official

NC 75 chopped back up 1936 Official